Experimental On Complexing Absorption Of NO Using Fe^ⅡEDTA Solution And Reduction With （NH₄）₂SO₃ Solution

The combustion of coal produces a large number of nitrogen oxides, triggering the ozone layer void, photochemical smog, acid rain, haze and a series of environmental problems, which causes serious effects on human health and ecological environment,and has become the key air pollutant must be controlled during the 13th Five Year Plan of China. Fe-based complexes represented by FeⅡEDTA have a good effect on complexation and absorption properties of NO, which has aroused the concern of scholars at home and abroad. FeⅡEDTA and NO molecules can directly transfer NO from the gas phase into the liquid phase, which greatly improves the NO solubility and overcomes the problem of the liquid phase mass transfer that’s limited in the NO wet absorption,so that direct wet absorption has well prospect with a strong application prospects. At the same time, wet ammonia desulfurization technology has been widely used in SO2 control field of coal-fired flue gas. The main components of desulfurization liquid produced by ammonia desulfurization are (NH4)2SO3, which can be reduced to N2 by the reduction characteristic of (NH4)2SO3, achieving simultaneous desulfurization and denitrification. Meanwhile, it can recycle the mixed products of ammonium sulfate and ammonium nitrate and have great application potential. Based on the existing research and the field treatment process, the effects of preparation parameters and working conditions on the NO absorption of FeⅡEDTA were investigated. The macroscopic kinetics of absorption of NO and the reaction rate of the FeⅡEDTA/(NH4)2SO3 mixed solution to absorb NO were investigated. The main conclusions were described as follow.Firstly, the influences of the preparation parameters ( pH value, liquid-gas ratio,initial concentration of the FeⅡEDTA solution, FeⅡ/EDTA molar ratio), the operation conditions ( temperature,oxygen content,gas flow rate,NO concentration of the entrance) were investigated. The FTIR and Raman spectroscopy were used to characterize the absorption solution. The results showed that the pH value and the initial concentration of the FeⅡEDTA solution effected the complex absorption of NO were significant, the volume of the FeⅡEDTA solution and the FeⅡ/EDTA molar ratio showed less important. A higher temperature and oxygen content were not favorable to the absorption of NO. NO absorption decreased by 71.69% and 63.3% when the temperature increased from 30 to 60℃ and the oxygen content increased from 0 to 6%.The effects of the gas flow rate and the entrance NO concentration on absorption of NO were insignificant. The optimal conditions of absorbing NO were determined: The pH value was 7, the liquid-gas ratio was 2.87 L/m3, the initial concentration of the FeⅡEDTA solution was 0.02 mol/L, the FeⅡ/EDTA molar ratio was 1:1, the temperature was at 30℃, the gas flow rate was 900 mL/min, the concentration of O2 volume should be 0%. NO absorption and the maximum removal efficiency were 0.727 mol/mol and 96.23%, respectively. FTIR characterization results show that the effective binding of Feu and EDTA to FeⅡEDTA in the precursor is the main reason for the significant enhancement of the solubility of NO in solution.Secondly, The reaction rate constants k1 and k2 of FeⅡEDTA complexes were calculated by the study of the macroscopic kinetics of NO absorption by FeⅡEDTA and the correlation kinetic parameters were determined. The average of reaction rate constant k1 and k2 were calculated to be 6.82 x105 L/(mol·s) and 2.54x109 L/(mol s),respectively. In addition, the order of the enhancement factor β was 102. It also clarifies the control steps of absorbing NO process in the range of different FeⅡEDTA concentration, and provides the data reference for the study of FeⅡEDTA/(NH4)2SO3 absorption reduction and removal of NO.At the end, The addition of (NH4)2SO3 plays an important role in the NO absorption and the reduction of FeⅡEDTA(NO) in the system. The time of NO removal of FeⅡEDTA is prolonged and the maximum removal rate of NO is 96.68%, NO removal efficiency remained at 70% or more in 600 min. At the same time, the recoveries of EDTA, Fe(OH)3 and Na2SO4 were 68.84%, 83.1% and 75.95%respectively by alkaline hydrolysis and acid precipitation. The remaining EDTA iron ammonium salt was used as photographic material and thinner,(NH4)2SO4 as fertilizer raw material. Therefore, waste liquid is effectively treated and reused.